1. Technical Field
The following embodiment relates generally to a bandpass filter, and more particularly to a bandpass filter that provides a wide range of gain control.
2. Description of the Related Art
A switched gmC N-path bandpass filter may automatically vary the signal pass-band of a bandpass filter by varying an input clock frequency. The switched gmC N-path bandpass filter has a structure suitable for processing a narrow-band signal over a wide frequency band, and has been recently developed.
However, the switched gmC N-path bandpass filter has some technical problems when applied to a high-performance communication receiver. In detail, it is difficult to impart the existing switched gmC N-path bandpass filter with a constant transfer characteristic in gain control due to the characteristics of circuit implementation, and thus a gain control function has not been implemented for input signals having a wide amplitude range.
The gain control function is an essential function because a receiver processes input signals within a wide signal amplitude range. When the gain control function is added in the switched gmC N-path bandpass filter, the linearity of the bandpass filter may be greatly decreased by distortion of the transfer characteristic of the filter, according to the method of implementation of the added gain control function. This is because the characteristic of the switched gmC N-path bandpass filter is changed in conjunction with gain control when the switched gmC N-path bandpass filter itself has the gain control function due to the change of the internal circuit of the switched gmC N-path bandpass filter. Therefore, it is difficult to precisely control the required gain depending on the change of the characteristic.
The Korean Patent Application Publication No. 10-2003-0048046 (disclosed on Jun. 18, 2003) disclosed a GmC filter for suppressing unwanted signals generated by a GmC compression stage.